HYDATIDS. 155 



apparently by minute internal buds or gemmules, 

 which grow on the membranous walls of the sac ; 

 on attaining to a certain size, they become detached, 

 and may be seen by means of a lens, floating in 

 the gelatinous fluid with which the sac is filled. 

 According to the observations of Mr. Youatt, in 

 allusion more particularly to the cerebral Irydatid, 

 when the fluid contained in the cyst is clear, the 

 internal membrane will appear, if examined with 

 a lens, to be covered with a countless multitude of 

 little grain-like bodies, disposed in regular lines, 

 and adhering by filmy particles. These he calls 

 eggs. None, however, are discoverable in the fluid 

 itself. But when the fluid is turbid, it will be found 

 full of apparently fibrous particles, which when 

 viewed through a microscope are resolved into 

 minute worms, many eggs being also intermingled; 

 but when a still more turbid and opaque state of 

 the fluid prevails, it is owing to an immense quantity 

 of these worms, while all the eggs or granules have 

 disappeared. " These worms," he says, " are about 

 half a line in length; the head is in the form of 

 a tetragon, (or four-sided figure,) with a circle of 

 rays at its summit, and a mouth on each of the 

 four sides ; the neck is short, and the body covered 

 with rings or wrinkles. They appear to swim with 

 great velocity and to be possessed of much activity. 

 They have also the peculiar property of issuing at 

 pleasure from and of returning to the cyst which 

 they inhabit. If the cyst be removed from the 



